Some non-chromecast solutions:
While Chromecast support itself is nice, for some people - like myself, just getting the audio to my stereo was enough (even if there is a lag of a few seconds).
DLNA and Pulseaudio
In that vein, I was using pulseaudio-dlna in Linux and sending audio to my TV/Stereo (all audio that is, not just WACUP or whichever audio player I happened to be using).
My slightly fiddly setup would is to start streaming with DLNA, then once that is going, I would use the remote control to go to launch ProjectM on my TV and get visuals going.
EDIT: @Dro just found the conversations on forums from 10 years ago re: DLNA, hope the other info is useful.
The downside is that Android may decide to kill the recieving app at some point.
You may have luck using windows DLNA support or even the windows pulseaudio builds and it's DLNA support (I'm not sure how easy or possible this last bit is).
KODI:
I used to use KODI to receive audio on my Android TV and play visuals, but a few years ago the visuals disappeared from the build for some reason.
ROC
ROC looks very promising for sending and receiving audio over the network (low latency and forward error correction are touted)
https://gavv.github.io/articles/roc-tutorial/Conclusion:
DLNA is the easiest thing to get going (and it wouldn't surprise me if a winamp plugin already exists) - it's laggy, but works.
ROC looks promising and provides a library, I've been able to run the reciever on my Android TV (for now had to sideload and it has no icon, though that is easily patched).